Folded tube for heat exchanger, and heat exchanger including such tubes

ABSTRACT

The invention relates to a tube for a heat exchanger, consisting of a metal strip having an inner face and an outer face, this strip having two extremities which are folded locally towards the inner face of the tube so as to form two borders ( 28, 30 ) placed one beside the other. Passages ( 38 ) are formed in at least one of the extremities of the metal strip for introduction of a brazing flux. These passages ( 38 ) can be formed in the two extremities of the metal strip, and offset with respect to one another. The passages extend over a distance greater than the height of the borders ( 28, 30 ) in such a way as to form an inlet ( 40 ) for the brazing flux.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a folded tube suitable for forming partof a heat exchanger such as a radiator for cooling a motor-vehicleengine, for example.

[0002] It relates more particularly to a folded tube for a heatexchanger, consisting of a metal strip having an outer face and an innerface, this strip having two extremities folded locally towards the innerface of the tube so as to form two borders placed one beside the other.

[0003] Tubes of this type are already known. After folding, they areassembled with spacers or fins, placed in a furnace and brazed. Thebrazing alloy is generally added by way of a plating of brazing alloyarranged on the outer face of the metal strip, while the inner face iscoated with an anti-corrosion plating.

[0004] In order to achieve high-quality brazing, it is necessary to adda brazing flux which has the function of protecting the metal againstoxidation during the brazing. According to the present-day technique,the brazing flux is deposited by immersion coating. This gives rise tothe situation that the two faces of the metal strip, both the inner faceand the outer face, are coated with brazing flux. After brazing,residues prejudicial to the internal corrosion resistance of theradiator are left behind.

[0005] The precise object of the present invention is a tube for a heatexchanger and a method of manufacturing this tube, embodiments of whichmay at least partially remedy these drawbacks.

BRIEF SUMMARY OF THE INVENTION

[0006] This can be achieved by the fact that passages are formed in atleast one of the extremities of the metal strip for introduction of abrazing flux. By virtue of these passages, the brazing flux canpenetrate between the side-by-side borders, which prevents themoxidizing.

[0007] According to a variant embodiment, passages are formed in the twoextremities of the metal strip. In this case, the passages at oneextremity are advantageously offset with respect to the passages of theother extremity of the metal strip.

[0008] According to one embodiment, the passages are produced byknurling of the extremities of the metal strip. The metal strip ispreferably folded by passing through a series of successive rollers, andthe knurling is carried out before passing through the forming rollers.

[0009] The passages can be formed substantially perpendicularly to theextremities of the metal strip or obliquely with respect to theseextremities.

[0010] The passages preferably extend over a distance greater than theheight of the borders in such a way as to form an inlet for the brazingflux.

[0011] The invention also relates to a heat exchanger, especially for amotor vehicle, comprising a bank of tubes alternating with coolingspacers, in which the tubes are in accordance with the invention.

[0012] Finally, the invention relates to a method of manufacturing atube for a heat exchanger by folding and brazing of a metal strip, thisstrip including an inner face and an outer face.

[0013] According to the method of the invention, a brazing flux issuitably deposited solely on the outer face of the tube, preferably byspraying.

[0014] Other characteristics and advantages of the present inventionwill emerge further upon reading the description which follows of anembodiment example given purely illustratively with reference to theattached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In these figures:

[0016]FIG. 1 is an overall view of a heat exchanger for which a tube inaccordance with the present invention is intended;

[0017]FIG. 2 is a view in cross section of a tube in accordance with thepresent invention;

[0018]FIGS. 3 and 4 are partial views on an enlarged scale, respectivelyin cross section and from above, of the tube represented in FIG. 2; and

[0019]FIG. 5 is a partial view, on an enlarged scale, in perspective, ofthe tube represented in FIGS. 2 to 4.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The heat exchanger represented in FIG. 1 comprises a tube bank 10mounted between two manifold chambers 12 and 14. The bank 10 consists ofa multiplicity of tubes 16 arranged parallel to each other andalternating with spacers 15. These spacers, also called fins, are of thecorrugated type. They are formed from metal foil which is folded so asto constitute corrugations. Hence, a spacer 15 arranged between twoadjacent tubes 16 comes into contact with two tubes via end regions ofthe corrugations.

[0021] The heat exchanger further includes two checks 17, also calledcrosspieces, which frame the tube bank and are arranged parallel to thetubes 16.

[0022] The pieces which constitute the exchanger are held assembled on atable (not represented) and pressure is exerted on the checks 17 in thedirection of the arrows F so as to hold the tubes 16, spacers 15 andchecks 17 respectively with a view to the brazing operation.

[0023] The tube 16 represented in FIG. 2 is produced from a metal strip,for example of aluminum, folded in several successive operations byvirtue of rollers according to a known technique. This is a flat tubewhich features a substantially rectangular, very much flattened, sectioncomprising two large faces 18 and 20 linked by two semi circular faces21.

[0024] The large face 18 consists of two parts 24 and 26 which arejoined together. The metal strip is folded at right angles to theextremities of the parts 24 and 26 so as to form side-by-side borders 28and 30 which bear on the large face 20, on the inside of the tube. Theseborders 28 and 30 have the function, on the one hand, of delimitingseparate circulation channels 32 and 34 for a fluid, and, on the otherhand, of constituting a distance piece between the two large faces 18and 20 so as to guarantee that they are parallel and flat.

[0025] In order to allow brazing of the tube, the metal strip is coveredexternally with a brazing plating (not represented), the inner facebeing covered with an anti-corrosion plating (not represented). As canbe seen, the borders 28 and 30 are placed one beside the other in such away that the gap which may remain between them is too restricted toallow a brazing flux to be brought in between these borders.

[0026] For this reason, in accordance with the invention, as can can beseen more particularly in FIGS. 3 to 5, passages 38 have been formed inthe borders 28 and 30. Although, in the embodiment described, passages38 had been provided in each of the two borders 28 and 30, it is alsopossible, according to a variant embodiment, to provide such passagesonly in one of the two borders.

[0027] In the embodiment example described, the passages 38 aresubstantially perpendicular to the large faces 18 and 20. Thischaracteristic is not essential, and it would also be possible, inaccordance with the invention, to provide passages arranged obliquelywith respect to these walls. Likewise, in the embodiment described, thepassages are straight-line, but they could also exhibit another shape,for example curved or sinusoidally shaped. As can be seen in FIG. 4, thepassages are preferably arranged alternately, one passage 38 of theborder 30 being arranged between two passages of the border 28, and viceversa.

[0028] Further preferably, as can be seen in FIG. 3, the length of thepassage 38 formed at the extremity of the metal strips is substantiallygreater than the height of the borders 28 and 30 in such a way as toconstitute an inlet 40 which facilitates the introduction of the brazingflux.

[0029] This brazing flux is arranged only on the outer face of the metalstrip, preferably by spraying, but it could also be added by anothertechnique, for example by immersion coating.

1. Tube for a heat exchanger, consisting of a metal strip having aninner face and an outer face, this strip having two extremities whichare folded locally towards the inner face of the tube so as to form twoborders (28, 30) placed one beside the other, characterized in thatpassages (38) are formed in at least one of the extremities of the metalstrip for introduction of a brazing flux.
 2. Tube according to claim 1,characterized in that passages (38) are formed in the two extremities ofthe metal strip.
 3. Tube according to claim 2, characterized in that thepassages (38) of one extremity are offset with respect to the passages(38) of the other extremity of the metal strip.
 4. Tube according toclaim 1, characterized in that the passages (38) are produced byknurling of the extremities of the metal strip.
 5. Tube according toclaim 4, characterized in that the metal strip is folded by passingthrough a series of successive rollers, and in that the knurling iscarried out before passing through the forming rollers.
 6. Tubeaccording to claim 1, characterized in that the passage (38) areproduced substantially perpendicularly to the extremities of the metalstrip.
 7. Tube according to claim 1, characterized in that the passages(38) are produced obliquely with respect to the extremities of the metalstrip.
 8. Tube according to claim 1, characterized in that the passagesextend over a distance greater than the height of the borders (28) and(30) in such a way as to form an inlet (40) for the brazing flux. 9.Tube according to claim 1, characterized in that the outer face of themetal strip is covered with a plating of brazing alloy.
 10. Heatexchanger, especially for a motor vehicle, comprising a bank of tubes(16) alternating with cooling spacers (15), characterized in that thetubes are in accordance with claim
 1. 11. Method of manufacturing a tubefor a heat exchanger, as defined in claim 1, by folding and brazing of ametal strip, this strip including an inner face and an outer face,characterized in that a brazing flux is deposited solely on the outerface of the tube.
 12. Manufacturing method according to claim 11,characterized in that the brazing flux is deposited on the outer face ofthe metal strip by spraying.